Oxygen dissolved in water, even in extremely low concentrations, can cause severe corrosion problems for various metals. At a level of only one part per billion the corrosion potential of oxygen is significant, and it is sufficient to corrode many metals and alloys in contact with water. For example, oxygen is believed to be responsible, at least in part, for the cracking which occurs in the keyways of steam turbines, the denting of nuclear boiler tubing, and the pitting which can occur in fossil fuel boilers and associated equipment.
Oxygen corrosion can be reduced by metering various oxygen scavengers, such as hydrazine, into the water. However, it is necessary to accurately measure the oxygen content of the water to avoid using too little oxygen scavenger, which may result in corrosion, or too much oxygen scavenger, as some scavengers themselves can break down to form various products which can corrode metal if they are used in excess.
The sensitivity of present meters for measuring oxygen, however, is only about one or two parts per billion of oxygen and at that level they are not very accurate. Thus they cannot be relied upon to indicate whether or not oxygen has been adequately reduced to control the corrosion process. Moreover, present oxygen meters are bulky and cannot be used in small spaces such as the core of a nuclear reactor.